Nature exposure impacts affect and brain activation in health and major depression

Considerable research attention has been devoted to the negative impact of urban compared to natural environments on mental health and well-being. Recent studies have addressed the neurobiological underpinnings but have mostly focused on post-hoc effects. How brain activation is acutely changed during nature exposure has barely been investigated. This study sought to assess how affect and cortical activation patterns in a natural environment differ from those in an urban area and how this is influenced by depressive symptoms. To this end, portable functional near-infrared spectroscopy (fNIRS) was used in a 16x16 optode layout to measure cortical activation during a 10-min stay in either a natural or urban environment in 16 patients with major depression and 16 healthy controls. Effects on affect and cognition were explored using questionnaires. Across the whole sample, nature exposure reduced negative affect. When fNIRS channels were allocated to anatomically informed regions of interest, we found decreased spontaneous neural activity in the left ventrolateral prefrontal cortex (PFC) and the right superior temporal gyrus during nature compared to urban exposure, albeit uncorrected for multiple comparisons. Using a data-driven approach, cluster-based permutation testing confirmed a reduced activation of the left PFC during nature exposure. Brain activation remained uninfluenced by depression or antidepressant medication, but depressive symptoms correlated with a reduction of negative affect. Given the limited sample size, these data should be treated as exploratory and only preliminary evidence to suggest that time spent in nature might reduce the strain on brain regions involved in regulating negative emotions and social stress, largely unaffected by depression. These findings warrant replication in larger, future studies.